The present invention relates to a sputtering target for forming a thin film of a semiconductor device. Specifically, the invention relates to a copper-manganese-alloy sputtering target having a self-diffusion suppression function for forming semiconductor copper alloy line.
Conventionally, Al alloys, of which specific resistance is roughly 3.0 μΩ·cm, were used as a line material of semiconductor elements. However, a copper line having lower resistance, of which specific resistance is roughly 2.0 μΩ·cm has been put into practical use with miniaturization of lines. A Copper line is generally formed by forming a diffusion barrier layer of such as Ta or TaN in lines or line via holes and then forming a film of copper by sputtering. Copper having a high purity of 5N to 6N is usually produced from electrolytic copper having a purity of about 4N (excluding gas components) as a crude metal by a wet or dry purification process, and the purified copper is used as a sputtering target.
Though copper is very effective as a semiconductor line as described above, copper itself is a very active metal and easily diffuses, and therefore causes a problem of contaminating a Si substrate or its periphery through the semiconductor Si substrate or the insulating film thereon. In particular, with progress in miniaturization of lines, the problem cannot be sufficiently prevented by only the conventional diffusion barrier layer of Ta or TaN, and copper line materials themselves also need to be improved. Accordingly, as a copper line material, a copper alloy having a self-diffusion suppression function has been proposed, which is prepared by adding manganese (Mn) to copper (Cu), by forming a barrier layer by itself through a reaction of Mn in the Cu—Mn alloy with oxygen in an insulating film (e.g., Patent Literature 1).
The sputtering target mentioned above is usually bonded to a backing plate with a bonding material and the like. After the use of the target, it is necessary to stop the sputtering apparatus and replace the used target with a new one. In order to reduce the manufacturing cost by shortening this stop time (down time) as much as possible, an increase in the thickness of the target itself has been demanded by unifying the target and the backing plate. In such an integrated target, however, the mechanical strength is insufficient to prevent deformation such as a warpage of the target during sputtering.
In order to overcome such a disadvantage, for example, Patent Literature 2 discloses a technology; that is, even in sputtering at high output, it is possible to prevent the deformation such as a warpage of an integrated structure-type target composed of a target and a backing plate made with the same material by increasing the mechanical strength through plastic working of the target. This technology, however, has a problem that a change in conditions of plastic working for increasing the mechanical strength of the entire target varies the sputtering characteristics of the target itself, resulting in not being able to achieve desired product performance.
Patent Literature 3 describes a technology of preventing occurrence of coarse particles by forming a cavity by irradiating a non-erosion portion of a sputtering target with laser light to reduce the hardness of the cavity bottom compared to that of the surface of the non-erosion portion. This technology softens the melting portion through laser irradiation to reduce the hardness of the cavity bottom compared to the surface of the non-erosion portion and is not a technology of increasing the strength of a target for inhibiting the target from being deformed during sputtering.